uva 11466 rte

#include <bits/stdc++.h>
using namespace std;
#define test int t; cin>>t; while (t--)
#define ll long long int
#define maX 1000008
bool marked[maX];
void sieve()
{
    marked[0]=1;
    marked[1]=1;
    for(ll i=4;i<=maX;i+=2)
    {
        marked[i]=1;
    }
    for(ll i=3;i<=maX;i+=2)
    {
        if(marked[i]==0)
        {
            for(ll j=i*i; j<=maX; j+=i+i)
            {
               marked[j]=1;
            }
        }
    }
}
int main()
{
   sieve();
   ll a,c,d,e,f,i,j,k,l;
   while(cin>>a && a)
   {
       c=sqrt(a)+1;
       d=0;
       if(c%2==0) c--;
       for(i=c;i>=3;i-=2)
       {
           if(marked[i]==0 && a%i==0)
           {
               d=i;
               break;
           }
       }
       if(d==0 && a>2)
       {
           if(a%2==0)
           {
               d=2;
           }
       }
       if(d==0) cout<<-1<<endl;
       else cout<<d<<endl;
   }


   return 0;
}